Re: [RFC PATCH 4/4] KVM: vmx: add support for emulating UMIP

[Paolo Bonzini]

On 13/07/2016 11:21, Yang Zhang wrote:
>>
>> +    if ((cr4 & X86_CR4_UMIP) && !boot_cpu_has(X86_FEATURE_UMIP)) {
>> +        vmcs_set_bits(SECONDARY_VM_EXEC_CONTROL,
>> +                  SECONDARY_EXEC_DESC);
>> +        hw_cr4 &= ~X86_CR4_UMIP;
>> +    } else
>> +        vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL,
>> +                SECONDARY_EXEC_DESC);
>> +
> 
> Since the faults based on privilege level have priority over VM exits.
> So we don't need to enable/disable SECONDARY_EXEC_DESC dynamically.
> Instead, we can set it unconditionally.

I'm setting it dynamically because it slows down LGDT, LLDT, LIDT and LTR.

Paolo